The invention relates generally to borehole probes of the type used to perform tasks or acquire data within the borehole. More particularly the present invention relates to probes that enable improved determination of probe depth information.
Downhole operations of the type practiced in the oil and gas exploration and recovery industries typically utilize probes to gather information and/or perform desired functions or operations in cased and open boreholes. In such operations, it is important to have depth information so that the data gathered can be known with respect to the depth from which the data was obtained or so that an operation can be performed at a desired depth.
Wireline probes are in communication with surface instrumentation, wherein the probe is conveyed into and out of the borehole using electric wireline. Other probes, such as the type conveyed on drill pipe or remote probes, are generally self-powered and are not in communication with surface instrumentation. In each case, however, improvement in obtaining depth information is desired.
Accordingly, the invention relates to probes for traversing a borehole having a plurality of benchmarks located therein at known depths.
In a preferred embodiment, the probe includes at least one pressure vessel having a depth reference point and depth determining devices associated with the vessel for enabling determination of data corresponding to the instantaneous depth of the depth reference point of the pressure vessel.
In a preferred embodiment, the depth determining devices include a clock, and computer memory for storing depth information corresponding to the depths of the benchmarks. A first sensor senses the benchmarks within the borehole relative to the depth reference point of the pressure vessel and generates output data corresponding to the identity of the sensed benchmarks. A comparator compares the sensed benchmark identification data to the stored depth information to match the sensed benchmark identification data to corresponding benchmark depths and generates signals corresponding to the depth data of the depth reference point of the pressure vessel at the time of passage of the depth reference point of the vessel. A second sensor senses the displacement of the depth reference point of the pressure vessel relative to each benchmark and generates output data corresponding to the displacement of the depth reference point of the pressure vessel relative to the most recently sensed benchmark. An analyzer analyzes the depth data of the most recently sensed benchmark and the output data corresponding to the displacement of the reference point of the pressure vessel relative to the most recently sensed benchmark to yield data corresponding to the instantaneous depth of the depth reference point of the pressure vessel.
In yet another aspect the invention relates to a method of determining the instantaneous depth of a probe in a borehole.
In a preferred embodiment, the method includes the steps of sensing the presence of a downhole benchmark having a known depth, sensing the displacement of the probe relative to the benchmark relative to the time of passage, and combining the displacement of the probe with the known benchmark depth to yield the instantaneous depth of the probe.